1) Field of the Invention
The present invention generally relates to controlled access systems for controlling the access to select users of equipment, and more particularly, to magnetic-based key access systems for controlling the access to select users of medical equipment.
2) Discussion of Related Art
Magnetically encoded cards have been used successfully for years to help control access to machines, doors, and locks. So called magnetic locks were originally mechanical locking devices. This type of lock includes magnetically controllable tumblers. A magnetic key used with this lock has embedded therein permanent magnets arranged in a prescribed pattern. If the pattern of the magnets within the key match the combination of the lock, the fields of each magnet exactly align with the tumblers of the lock. The field strength and field orientation of each aligned magnet within the “correct” key causes the tumblers to displace to a mechanically-open position. The tumblers of the lock are spring-biased and the magnets displace each tumbler against the action of each spring. The spring bias returns each tumbler to the locked position when the key is removed. Furthermore, if the device being controlled is electric, then an appropriate electric switch operating the device becomes moveable only when the tumblers move to an open position.
One benefit of this type of magnetic key locking system is that a typical key-slot or keyhole is not required to actuate the lock. The lock may be designed so that the magnetic key need only be positioned against a surface that lies adjacent to the tumblers of the lock. This is a great benefit for use in corrosive areas or areas where environmental conditions do not favor the delicate tumbler mechanisms of a lock. Also, if the tumblers are not physically accessible, they cannot be picked in a traditional manner, making this type of lock system more secure than conventional locks.
Unfortunately, mechanical locks have their limitations. Disadvantages include the expense of manufacture and the fact that many applications for this type of lock are electrically controlled, such as computer equipment, electrical medical devices, lighting, etc. The latter disadvantage led to the development of a magnetically-operated lock that uses electronic magnetic-field detecting devices which effectively replace the mechanical tumblers used in earlier lock versions, described above. Such magnetic-field detecting devices include reed switches and more reliable, more accurate and durable Hall effect sensors in an IC package.
A Hall effect sensor is a well known electronic device that can be used to detect the presence of a magnetic field. The Hall effect refers to the potential difference (Hall voltage) on the lateral sides of an electrical conductor crossed by an electric current when a magnetic field is applied perpendicularly. By measuring the lateral voltage potential, the strength and field orientation of the adjacent magnet can be determined. Such Hall effect sensors can be used to measure very small and slow fluctuations in a magnetic field, down to a hundredth of a gauss.
With the introduction of electronic magnetic-field sensing devices, key-card controlled access systems could be more reliable, less expensive and provide a greater number of key-combinations than with the above-described magnetically-controlled mechanical tumbler security system. The electronic magnetic-field sensors can also more directly and more reliably control the electronic security device whose access is being controlled.
Such key-access systems using electronic magnetic-field sensing devices generally provide consistent, accurate and reliable use and are generally durable in many different types of harsh environments, except one-magnetic environments.
On a regular basis, hospitals and clinics use a variety of electronic devices, many of which emit strong electromagnetic energy. Such strong-emitting devices include MRI units, monitors and defibrillators. Unless property shielded, these and almost every electronic device used everyday within the medical environment emits a certain amount of electromagnetic energy. The emitted electromagnetic energy creates weak and strong magnetic fields which can affect the operation of other electronic devices operating nearby. One type of device that could easily be affected by these fields is magnetically-controlled access systems which are relying on magnetic-field sensing components. Even relatively weak magnetic fields could interfere with the operation of the Hall-effect sensors and thereby prevent the access control device from accurately reading a key card. This magnetic interference could either provide improper access to an unauthorized user or prevent access to legitimate users.
It is a first object of the present invention to provide an access control system that overcomes the deficiencies of the prior art.
It is a second object of the present invention to provide an access control system that allows an authorized individual access to select and predetermined mode of operation to an electrical device.
It is another object of the present invention to provide an access control system that includes provisions to control and mitigate the effects of any outside interference caused by nearby electromagnetic fields.